This invention relates to the field of passive righting systems for mobile payloads, specifically systems that return a payload to a known orientation after unknown motion, for example after being launched through the air. Many electrical and mechanical systems rely on initial orientation for proper functioning. For example, cameras rely on being pointed at the scene of interest. Communications equipment can rely on antenna being pointed toward the transceiver. Hopping robots must have their hopping actuator pointed at the earth. Such systems are conveniently oriented by careful prepositioning. Prepositioning gives way to complicated balance, control, and recovery mechanisms when the system must be moved. Recovery mechanisms are especially important when the motion of the system can not be tightly controlled, such as when the system is dropped or launched, or encounters unpredictable obstacles.
Mechanical recovery mechanisms can require significant mechanical complexity and cost, and can consume significant power in operation. A well known contemporary example of a mechanical recovery or righting system is that used on the Pathfinder mission to Mars. The lander was a tetrahedron with three of the triangular sides hinged to the edges of the fourth side. Actuation of all three panels rolled the tetrahedron onto its base, independent of its initial orientation. This system does not need sensors to sense orientation, but does require significant power to right the lander. Power in many mobile systems is available only in trade for cost, expense, range, or functionality, so power-intensive techniques like that on the Pathfinder lander are undesirable for many applications.
Some toys are made with a measure of self-righting. The toy has a convex-everywhere shape, and is weighted so that the center of gravity of the toy is below the geometric center only when the toy is in a preferred orientation. This approach has the advantage of requiring no sensing or orientation, no energy input other than gravity, and no mechanical actuation. The final orientation can be less stable than desired for some applications because minor deviations from the preferred orientation do not result in significant gravity-induced moments to correct the deviation. Further, the convex-everywhere shape prevents reliable operation on slopes (since a convex-everywhere shape readily rolls down slopes). Accordingly, this technique is not suitable for applications where stability is needed, especially where stability is needed on varying terrain including slopes.
Accordingly, there is a need for an apparatus that can return a payload to a known orientation after unknown motion, without requiring external power or complex mechanical systems, that is stable even on sloped terrain.